The present invention relates to the alignment and optical coupling of the end of an array of optical fibres, such as in ribbon fibre, with waveguides in an optical device, such as an active semiconductor optical device or a passive device.
Optical fibres are commonly used to interconnect optical devices of various forms, including passive waveguide structures in silica and silicon and active semiconductor devices. Attaching optical fibres to optical devices is a technical challenge, particularly when attaching an array of optical fibres, for example in the form of ribbon fibre.
A well known way of attaching ribbon fibre to a passive, multi-channel optical device, for example an arrayed waveguide grating (AWG), involves mounting the end of the ribbon fibre in a fibre block assembly. FIG. 1 is an end view of a known form of fibre block assembly 1 comprising two blocks 2 bonded together. An array of fibres 3 are mounted between the two blocks 2 in arrays of v-grooves 4 formed in the opposed bonded surfaces 5 of the blocks 2. The fibre block assembly 1 serves to fix the relative positions of the fibres 3 in the array to a tolerance of, say, around xc2x10.5 xcexcm. The end surface of the fibre block assembly 1 is usually polished to an optical surface, either at normal incidence to the optical axes of the fibres or at an angle, if required.
A known way of using the fibre block assembly 1 of FIG. 1 to couple the optical fibres 3 to a passive optical device such as an AWG is known as xe2x80x9cbutt couplingxe2x80x9d. FIG. 2 is a side view illustrating the fibre block assembly 1 butt coupled to a passive optical device 6 in which there are waveguides 7. The polished end surface 8 of the fibre block assembly 1 and the polished surface 9 of the optical device 6 are brought into contact, or close proximity, commonly with a thin layer of optically clear adhesive 10 at the interface between the fibre block assembly 1 and the optical device 6. Prior to curing of the adhesive 10, the fibre block assembly 1 and the optical device 6 may be relatively aligned in the directions perpendicular to the optical fibres 3, that is in the directions up and down in FIG. 2 and into and out of the paper. However, the alignment in the direction in which the fibres 3 extend is fixed and may not be adjusted.
Butt coupling is unsuitable when it is important to avoid physical contact between the optical fibre and the optical device. This is the case, for example, with many active optical devices, such as those made of a semiconductor such as indium phosphide. Contact is also undesirable for optical devices having a fragile thin film coat.
The purpose of the present invention is to provide for alignment of an array of optical fibres with an optical device which allows alignment in a direction perpendicular to the optical axes of the optical fibres to be achieved more easily and/or which allows adjustment of the alignment along the direction in which the fibres extend.
According to a first aspect of the present invention, there is provided a method of aligning the end of an array of optical fibres with waveguides in an optical device, comprising: mounting the end of the array of optical fibres in a fibre block assembly comprising at least a first block, the first block having an array of grooves in a grooved surface of the block, the optical fibres being mounted in the grooves, the fibre block assembly further having at least one guide surface on the first block on the same side as the grooved surface at a predetermined level with respect to the axes of the array of optical fibres; supporting the optical device on a support surface of a bench, which bench has at least one guide surface extending from the support surface, by the surface of the optical device proximate to the waveguides; aligning the end of an array of optical fibres with the waveguides in the optical device by moving the fibre block assembly with the at least one guide surface of the first block in contact with the at least one guide surface of the bench; and fixing the fibre block assembly to the bench after said aligning of the end of the array of optical fibres with the waveguides in the optical device.
According to a second aspect of the present invention, there is provided a method of aligning the end of an array of optical fibres with waveguides in an optical device, comprising: mounting the end of the array of optical fibres in a fibre block assembly comprising a first block having an array of grooves in a grooved surface of the first block and a second block fixed to the first block with a surface having no grooves facing the grooved surface of the first block and with the fibres mounted between the blocks in the grooves, the fibre block assembly further having at least one guide surface on the second block on the same side as said surface facing the grooved surface of the first block at a predetermined level with respect to the axes of the array of optical fibres; supporting the optical device on a support surface of a bench, which bench has at least one guide surface extending from the support surface, by the surface of the optical device proximate to the waveguides; aligning the end of an array of optical fibres with the waveguides in the optical device by moving the fibre block assembly with the at least one guide surface of the first block in contact with the at least one guide surface of the bench; and fixing the fibre block assembly to the bench after said aligning of the end of the array of optical fibres with the waveguides in the optical device.
According to a third aspect of the invention, there is provided a coupling assembly optically coupling an array of fibres to an optical device, comprising: the optical device having a plurality of waveguides and having a surface proximate to the waveguides at a predetermined level with respect to the axes of the waveguides; a fibre block assembly mounting the end of the array of optical fibres, the fibre block assembly comprising at least a first block, the first block having a grooved surface defining an array of grooves, the optical fibres being mounted in the grooves, the fibre block assembly further having at least one guide surface on the first block on the same side as the grooved surface at a predetermined level with respect to the axes of the array of optical fibres; and a bench having a support surface on which the optical device is fixed by the surface of the optical device proximate to the waveguides, and at least one guide surface extending from the support surface, at a predetermined level with respect to the support surface, the at least one guide surface of the bench having the fibre block assembly fixed thereon by the at least one guide surface of the fibre block assembly, with the array of optical fibres aligned with the plurality of waveguides of the optical device.
According to a fourth aspect of the invention, there is provided a coupling assembly optically coupling an array of fibres to an optical device, comprising: the optical device having a plurality of waveguides and having a surface proximate the waveguides at a predetermined level with respect to the axes of the waveguides; a fibre block assembly mounting the end of the array of optical fibres, the fibre block assembly comprising at least a first block having a grooved surface defining an array of grooves and a second block fixed to the first block with a surface having no grooves facing the grooved surface of the first block and with the optical fibres mounted between the blocks in the grooves, the fibre block assembly further having at least one guide surface on the same side as said surface facing the grooved surface of the first block at a predetermined level with respect to the axes of the array of optical fibres; and a bench having a support surface on which the optical device is fixed by the surface of the optical device proximate to the waveguides, and at least one guide surface extending from the support surface, at a predetermined level with respect to the support surface, the at least one guide surface of the bench having the fibre block assembly fixed thereon by the at least one guide surface of the fibre block assembly with the array of optical fibres aligned with the plurality of waveguides of the optical device.
The provision of at least one guide surface on the fibre block assembly and the bench assists alignment in a direction perpendicular to the optical axes of the optical fibres because the contact between the guide surfaces fixes the alignment in one direction perpendicular to the optical axes of the optical fibres. The alignment is achieved simply by bringing the guide surfaces into contact without any active adjustment being necessary.
Also, the provision of guide surfaces allows the alignment of the end of the array of optical fibres to be adjusted in the direction along which the fibres extend. The contact between the guide surfaces allows the fibre block assembly to be guided along the bench in a controlled manner during the alignment process. The method also allows the alignment of the array of optical fibres to be adjusted laterally of the array, that is in the direction in which the array repeats. Accordingly, the method allows the end of the array of fibres to be positioned and subsequently fixed at a position in close proximity to the optical device but without physical contact. This is a particular advantage in the case of active semiconductor optical devices and other devices which are fragile, for example because of the presence of an optical thin film. Nonetheless the method may be used with any type of optical device. The method allows the optical fibres and the optical device to be butt coupled in which case the primary advantage is the fixing of alignment in one direction by the contact between the guide surfaces.
The vertical position of the array of optical fibres relative to the optical device, that is perpendicular to the direction of the optical axes of the fibres and to the direction in which the array repeats, is fixed by the contact between the guide surfaces of the fibre block assembly and the bench. To achieve vertical alignment, preferably the axes of the waveguides of the optical device are at a distance relative to the surface of the optical device on which the optical device is supported on the bench equal to the sum of the distance, if any, of the axes of the optical fibres relative to the at least one guide surface of the fibre block assembly plus the distance, if any, of the guide surface of the bench relative to the support surface.
The distance of the axes of the waveguides relative to the proximate surface of the optical device is known, because this may be controlled during manufacture of the optical device. The distance of the axes of the optical fibres relative to the at least one guide surface of the fibre block assembly and the distances of the at least one guide surface of the bench relative to the support surface may be controlled by suitable design of the fibre block assembly and the bench. This is particularly easy for the assembly if it is formed on the same side as the grooved surface, for example by being the grooved surface, or by being offset by a known amount from the grooved surface, e.g. by being etched from, or deposited on, the grooved surface. In particular, it is possible to control these distances to achieve vertical alignment with a desirable tolerance of at least xc2x10.5 xcexcm.
The use of a bench as an intermediate element between the fibre block assembly and the optical device allows accommodation of any difference between (a) the distance, if any, of the axes of the optical fibres relative to the at least one guide surface of the fibre block assembly and (b) the distance of the axes of the waveguides from the surface on which the optical device is supported. This may be achieved simply by selection of the distance between the support surface and the at least one guide surface of the bench. Thus the use of a bench as a separate intermediate element greatly eases the alignment process and avoids any need to provide either one of the optical device and the fibre block assembly with any complicated structures for aligning the optical fibres with the waveguides of the optical device.